In some configurations, a computer network has a primary station communicating with a number of secondary stations. A secondary station could be a modem designed to transmit and receive data over the cable television infrastructure. The primary station could be a modem server equipped with transmitters and receivers for exchanging data with modems over the cable television infrastructure.
In one type of network, the primary station sends information to the secondary stations on a downstream channel. The secondary station sends information to the primary station on an upstream channel. The master station controls the communication to and from the secondary station. As the number of secondary stations attached to the primary station increases, the control of the communication between the master station and the secondary station increases in complexity.
Protocols have been developed to assist in the control of such communication. One such protocol employs a polling discipline. The polling discipline provides multiple transmission devices shared access to a transmission medium. The primary station controls the access of secondary stations to the transmission medium by transmitting polls addressed to individual secondary stations in a sequential fashion. Typically, the master station limits the amount of data that can be sent in response to a poll to a fixed number of frames.
This approach suffers from two problems. First, in systems where the frame size is variable, the primary station has no knowledge, before transmitting a poll as to the nature or amount of data that will be returned in response to the poll. As a result, secondary stations with few large frames have better performance than secondary stations with many small frames.
Second, since the number of frames that can be sent in response to a poll is fixed, the system cannot quickly adapt to changing data traffic patterns on the shared medium. The only way to change the data traffic pattern is to change the number of frames that can be sent in response to a poll. This requires either reconfiguration of secondary stations or control signaling, either of which expends bandwidth and time.
An improved protocol is, therefore, highly desirable.